As Java applications grow in complexity, maintainability, scalability, and performance become critical challenges. To address these issues, Java 9 introduced the Java Module System (also known as Project Jigsaw), enabling strong encapsulation and modular design.

In this article, we will explore Java Modules, understand their advantages, and learn how to use them effectively for better code organization and performance optimization.

What Are Java Modules?

Understanding Java’s Modular System

A Java Module is a self-contained unit of code that defines:

  1. What it exports – Publicly accessible packages.
  2. What it requires – Dependencies on other modules.

Java Modules enforce strong encapsulation, ensuring that internal implementations remain hidden, preventing unintended dependencies.

Why Use Java Modules?

Java Modules provide several key benefits:

  • Better Encapsulation – Unlike traditional JAR files, modules explicitly define public vs. private components.
  • Faster Startup Times – The JVM loads only the necessary modules, reducing overhead.
  • Improved Security – Prevents unauthorized access to internal APIs.
  • Reduced Memory Footprint – Eliminates unnecessary dependencies.
  • Better Maintainability – Code is structured in clear, independent modules.

Creating a Java Module

Let’s create a simple Java Module named com.example.module.

1. Define module-info.java

A module is defined by a special file called module-info.java.

module com.example.module {
    exports com.example.module.service;
}

This module:

  • Exports the com.example.module.service package, making it accessible to other modules.
  • Hides other packages from external access.

2. Creating Module Packages

Organize your code as follows:

com.example.module/
 ├── module-info.java
 ├── com/example/module/service/HelloService.java

Now, define the HelloService class inside the com.example.module.service package:

package com.example.module.service;

public class HelloService {
    public void sayHello() {
        System.out.println("Hello from Java Module!");
    }
}

3. Consuming the Module

Create another module com.example.app that requires com.example.module:

module com.example.app {
    requires com.example.module;
}

Now, use the module in Main.java:

package com.example.app;

import com.example.module.service.HelloService;

public class Main {
    public static void main(String[] args) {
        HelloService service = new HelloService();
        service.sayHello();
    }
}

Compile and run:

javac -d out --module-source-path src $(find src -name "*.java")
java --module-path out -m com.example.app/com.example.app.Main

Performance Benefits of Java Modules

1. Faster Application Startup

By loading only required modules, Java Modules significantly reduce startup time compared to monolithic JAR applications.

2. Reduced Memory Usage

Unused classes are not loaded into memory, lowering heap consumption.

3. Strong Encapsulation Leads to Safer Code

Encapsulation prevents unintended dependencies, making applications more stable.

4. Efficient JIT Compilation

Java Modules help the Just-In-Time (JIT) Compiler optimize execution, improving runtime performance.

Best Practices for Java Modules

✅ Use Modules for Large Applications

  • Small projects may not need modules, but large applications benefit from better organization.

✅ Minimize requires transitive

  • Avoid unnecessary dependencies that increase module complexity.

✅ Keep Internal APIs Hidden

  • Use exports wisely to restrict access to internal code.

✅ Use provides ... with for Service Providers

  • The Service Provider Interface (SPI) allows modular plugins.

Example:

module com.example.module {
    exports com.example.module.service;
    provides com.example.module.service.HelloService
        with com.example.module.service.HelloServiceImpl;
}

Conclusion

Java Modules offer strong encapsulation, better performance, and modular design, making them an essential tool for modern Java applications.

Key Takeaways:

✔ Java Modules enforce strong encapsulation.
✔ Improves startup performance and reduces memory footprint.
✔ Prevents accidental dependencies and improves security.
✔ Essential for large-scale applications but optional for small projects.

By adopting Java Modules, developers can create efficient, scalable, and well-structured applications. Ready to modularize your Java code? 🚀